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November 2014

79 participants
77 discussions

[boost.variant] accessing variant with pattern-matching instead of visitors
by Roger 02 Nov '14

02 Nov '14

Hi! The CppCon 2014, Yuriy Solodkyy had an interesting talk "Accept no visitors"(*). It presents an alternative accessing technique for variant data-type. It basically use pattern matching syntax, similar to that in functional languages, instead of visitors. I think this would be a great benefit for boost::variant data-type... being able to access variables from the same scope, group states similar in behavior, and take care of the loop unrolling for dispatching oneself. Especially when using variant as polymorphism, like the other interesting CppCon 2014 talking, Jason Lucas "Polymorphism with Unions" (**) covered. Would it be worth to implement a tiny pattern-matching library for boost::variant itself? Has anyone elaborated with this? Thanks for any hints! /perrog * Yuriy Solodkyy "Accept no visitors, http://youtu.be/QhJguzpZOrk ** Jason Lucas "Polymorphism with Unions", http://youtu.be/uii2AfiMA0o

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by Johnny McCullough 01 Nov '14

01 Nov '14

I'm new to boost, and I'm wondering about the best / most efficient way to transfer a large dataset via boost::asio. I've retrieved a datasetfrom a database (Cassandra) and I'm using boost asio to provide a network service that responds to queries. So I have a client socket and a dataset. I have to iterate the dataset, perform some simple formatting (e.g. csv, json, xml), then write it out to the client socket. But there's a lot of data. Perhaps gigabytes. So my initial thoughts were the producer / consumer pattern - the producer writing to a streambuf and the consumer async_write-ing it out to the client's socket. But I'm not sure this is a good approach - I know that streambuf isn't threadsafe and so managing the streambuf with locks may well become a performance bottleneck. Obviously, I don't want to replicate what may be gigabyte(s) of data from a resultset into a buffer just so it can be written out to a socket, So should I write this data synchronously straight to the socket instead? What's the best approach to solving this kind of problem? thanks for your consideration

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